The world, they hold, comes into being when its substance has first been converted from fire through air into moisture and then the coarser part of the moisture has condensed as earth, while that whose particles are fine has been turned into air, and this process of rarefaction goes on increasing till it generates fire. Thereupon out of these elements animals and plants and all other natural kinds are formed by their mixture. The generation and the destruction of the world are discussed by Zeno in his treatise On the Whole, by Chrysippus in the first book of his Physics, by Posidonius in the first book of his work On the Cosmos, by Cleanthes, and by Antipater in his tenth book On the Cosmos. Panaetius, however, maintained that the world is indestructible. The doctrine that the world is a living being, rational, animate and intelligent, is laid down by Chrysippus in the first book of his treatise On Provide?ice, by Apollodorus in his -Physics, and by Posidonius. It is a living thing in the sense of an animate substance endowed with sensation ; for animal is better than non-animal, and nothing is better than the world, ergo the world is a living being. And it is endowed with soul, as is clear from our several souls being each a fragment of it. Boethus, however, denies that the world is a living thing. The unity of the world is maintained by Zeno in his treatise On the Whole, by Chrysippus, by Apollodorus in his Physics, and by Posidonius in the first book of his Physical Discourse. By the totality of things, the All, is meant, according to Apollodorus, (1) the world, and in another sense (2) the system composed of the world and the void outside it. The world then is finite, the void infinite.